A cordless telephone system and a FAX (abbreviation of facsimile) terminal attaining a dual-line adaptation function in a single unit (a function to control communication through two connected lines) are provided. These terminals attain simultaneous communication through two lines using a plurality of separate handsets, by containing two RF (Radio Frequency) communication modules in a base phone. Here, the cordless telephone system refers to a system allowing wireless communication between an apparatus for connection to an external line (base phone) and a telephone (handset).
Some conventional base phones with a dual-line adaptation function have a FAX function as a resource, however, one base phone has only one such resource. Therefore, if a request for calling a FAX function is made through one line while the FAX function operates in the other line, it has been impossible to respond to this request. As a result, exclusive processing of the request for calling the FAX function has been unavoidable.
Similarly, as to an answering and recording function (a function for recording and receiving a message, automatically actuated when a telephone call arrives), a cordless telephone allowing simultaneous recording through two lines has also been proposed. This is achieved by incorporating two different units responsible for the answering and recording function into the base phone. Therefore, a unit price of the base phone has been high.
In addition, a technique for operating a system for integrating two different communication networks has also been proposed (see Japanese Patent Laying-Open No. 2001-308877).
As the conventional base phone with a dual-line adaptation function includes two RF communication modules, the unit price has been high and not economical. Moreover, demand for a terminal (base phone) itself attaining the dual-line adaptation function has not been considerably great. Accordingly, when a terminal is developed as a dedicated dual-line-adapted model, depreciation of development cost has been difficult.
In addition, as compared with the base phone attaining a single-line adaptation function (a function to control communication through a single connected line), selection of products has been poor and user's choice has been limited. In the case of the terminal attaining the single-line adaptation function, the base phone including a resource of a type required by the user (such as a FAX function, an answering and recording function, or the like) may not be provided.
When a cordless telephone set A attaining the single-line adaptation function (implemented by a base phone A and a handset group A) is simply connected to Line (line) 1 and a cordless telephone set B attaining the single-line adaptation function (implemented by a base phone B and a handset group B) is simply connected to Line (line) 2, the following limitation is imposed.
First, it is assumed that a calling request is issued to one of Lines 1 and 2. If the calling request comes through Line 1, solely base phone A and handset group A make ringing sounds, and they have been unable to call telephone set B. In contrast, if the calling request comes through Line 2, solely base phone B and handset group B make ringing sounds, and they have been unable to call telephone set A.
In addition, if one of lines 1 and 2 is busy (for example, Line 1 is busy and Line 2 is idle (unused)), the terminal in telephone set A (base phone A or handset group A) cannot establish communication using Line 2. On the other hand, if Line 2 is busy and Line 1 is idle, communication from the terminal in telephone set B (base phone B or handset group B) using Line 1 is not allowed.
As to a call transfer function/INTERCOM (extension call) function, calling and call transfer from the terminal in telephone set A to the terminal in telephone set B through INTERCOM is not allowed, or calling and call transfer from the terminal in telephone set B to the terminal in telephone set A through INTERCOM is not allowed.
In the base phone incorporating resources such as one FAX function and one answering and recording function respectively, if requests for use of an identical resource are simultaneously made through both of Lines 1 and 2, only one request can be responded, because there is only one resource available. For example, when a calling request for FAX communication from Line 2 arrives during FAX communication through Line 1, a response to Line 2 is caused to wait until the FAX communication through Line 1 is completed. Though two resources of the same type may be prepared in order to avoid such a situation, a unit price for each of base phones A and B tends to be inevitably high.